1. Field
The present invention relates to a mask frame assembly for thin film deposition.
2. Description of Related Art
In general, organic light-emitting display devices have a larger viewing angle, better contrast characteristics, and a faster response speed than other display devices.
Organic light-emitting display devices generally have a stacked structure including an anode, a cathode, and an emission layer interposed between the anode and the cathode, and display images in color when holes and electrons, injected respectively from the anode and the cathode, recombine in the emission layer, thereby emitting light. However, it is difficult to achieve high light-emission efficiency with such a structure, and thus, intermediate layers, including an electron injection layer, an electron transport layer, a hole transport layer, a hole injection layer, or the like, are optionally additionally interposed between the emission layer and respective electrodes.
An intermediate layer including electrodes and an emission layer of an organic light-emitting display device may be formed by using various methods, for example, deposition. When an organic light-emitting display device is manufactured by using deposition, a fine metal mask (FMM) having the same pattern as a thin film to be formed is placed on a substrate, and a thin film material is deposited over the FMM to form the thin film with a desired pattern.
In general, a high-resolution FMM needs to be formed with high precision, and it should be very thin. However, when the mask is made thin, wrinkles may be generated.
That is, a size of a pattern of the high-resolution mask is very small. Accordingly, shadows, which may affect a thickness of a thin film to be deposited, should not exist. In order to reduce or minimize the shadows, the mask should be made very thin.
When the mask is thinned and extended in one axis, wrinkles may be generated in the mask. When the mask having wrinkles is aligned with and deposited on the substrate, an area where the mask has wrinkles and is unable to contact the substrate may be generated. Accordingly, a precision pattern might not be formed on such a non-contact area.
In general, height of the wrinkles may be about 500 to 700 μm and may vary according to a type of the mask and the degree of tensile force used. Wrinkles are generated due to structural instability of the mask and should be removed or minimized. When a thinly processed mask is extended, wrinkles are generated and grown at some point. It is difficult to accurately predict the onset of wrinkling.